The invention relates to improvements in torque transmitting apparatus, and more particularly to improvements in hydraulic torque converters which can be utilized with advantage in the power trains of motor vehicles, e.g., between the rotary output element of the prime mover (such as an internal combustion engine) and the input element (such as a shaft) of a change-speed transmission.
A conventional hydrokinetic torque converter in the power train of a motor vehicle normally comprises a housing which shares the angular movements of the output element (such as the crankshaft) of the engine, a pump which shares the angular movements of the housing, a turbine which can receive torque from the housing by way of a body of hydraulic fluid confined in the housing and being circulated by the vanes or blades of the pump, as well as an output member (e.g., a hub) which can receive torque from the turbine to transmit torque to a driven member such as the input shaft of the change-speed transmission. The torque converter can further comprise a bypass clutch or lockup clutch (hereinafter called bypass clutch) which, when necessary or desired, transmits torque directly between the pump or housing and the turbine. Still further, such conventional torque converter can also comprise at least one torsional vibration damper which operates in the power train between the housing and the output member.
In many conventional torque converters of the above outlined character, a portion of the bypass clutch is fixedly secured to the input of the torsional vibration damper. Reference may be had, for example, to published German patent application Ser. No. 199 63 236 A1. The piston of the bypass clutch is or can be riveted to the input of the torsional vibration damper and such input comprises two annular flanges. During actuation (engagement or disengagement) of the bypass clutch, the piston of the bypass clutch is caused to move axially and to thus frictionally engage or become disengaged from the housing of the torque converter. Such axial movement of the piston entails a movement of the output of the torsional vibration damper because the output is provided with gear teeth mating with complementary gear teeth on the hub of the torque converter.
It can happen that the mating gear teeth generate pronounced friction or that they jam. In fact, the tension between the input of the torsional vibration damper and the piston of the bypass clutch, and/or non-uniform engagement of the piston of the bypass clutch with the friction surface of the housing of the torque converter, can cause the development of excessive stresses, a cracking of cooperating parts and fatigue-induced breaks. Such undesirable phenomena are particularly likely to develop in the parts which are riveted to each other. Still further, excessive tension between the piston of the bypass clutch and the input of the torsional vibration damper is likely to develop when the piston is caused to frictionally engage the housing with attendant deformation (particularly in the axial direction of the bypass clutch) when the pressure of hydraulic fluid in the cylinder chamber for the piston increases, i.e., when the piston is called upon to transmit torque from the housing to the output of the torque converter by establishing a direct power transmitting path from the output element of the prime mover, through the housing of the torque converter and to the output of the latter, i.e., by bypassing the pump and the turbine of the torque converter.
The torsional vibration damper comprises coil springs or other suitable resilient elements which act in the circumferential direction of the input and output when the input turns relative to the output and/or vice versa. When the RPM of the torsional vibration damper is very high, the springs are held against radially outward movement under the action of centrifugal force. The means for preventing such radially outward movements of the springs are costly as well as bulky because they take up room as considered axially as well as radially of the damper. In order to achieve most satisfactory friction within the entire RPM range of the springs, it is necessary to establish an optimum relationship between the parts which can or should turn relative to each other, especially between the coil springs on the one hand and the input and/or output of the torsional vibration damper on the other hand.
It is often advisable to connect the torque converter to an axially elastic disc or wall which is attached to and receives torque from the output shaft of the prime mover (such as the crankshaft of the engine) in the power plant of a motor vehicle. The connection is normally established by resorting to threaded fasteners having shanks mating with internal threads provided in one of the torque converter and the disc. This normally involves individual application and tightening of each of a plurality of threaded fasteners. Such tightening is carried out by resorting to a suitable tool which can reach the fasteners through one or more access openings provided in the housing or bell of the change-speed transmission of the power train. The torque converter must be caused to turn, at least at intervals, in order to afford access to the fasteners. Such modes of affixing the torque converter to the torsional vibration damper and of mounting the damper in the torque converter are time-consuming and necessitate the hiring of highly skilled artisans. The situation is complicated because the installation of a torque converter in the power train of a vehicle also invariably necessitates the hiring of highly skilled artisans who are capable of carrying out the above outlined undertakings in addition to centering of cooperating moving (rotary) parts relative to the adjacent part or parts.